The gas most commonly used to inflate balloons is helium. Helium is a colorless and odorless gas that is lighter than air, allowing balloons filled with it to float. Its non-flammable nature makes it a safe choice compared to hydrogen, which is also lighter but poses explosion risks. Helium is a noble gas and is often used in party balloons, scientific applications, and even in medical equipment. Helium is also abundant in nature, primarily extracted from natural gas reserves, making it a popular fill gas for various types of balloons and decorative displays.